This invention relates generally to heat and pressure fusers for fixing color images an electrophotographic printing machines, and more particularly to a Release Agent Management (RAM) therefor.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent image on the photoconductive member. The toner attracted to a donor roll is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip.
The heated fuser roll is usually the roll that contacts the toner images on a substrate such as plain paper. In any event, the roll contacting the toner images is usually provided with an abhesive material for preventing toner offset to the fuser member. Three materials which are commonly used for such purposes are PFA.TM., Viton.TM. and silicone rubber. All of these materials, in order to maintain their abhesive qualities, require release agents specific to the material.
Various methods are known for applying release agent materials to a fuser member such as a heated fuser roll. One such system comprises a Release Agent Management (RAM) system including a donor roll which contacts the fuser member to which the oil or release agent material is applied. The donor roll also contacts a metering roll which conveys the oil from a supply of oil to the donor roll. With such a system, it is customary to use a metering blade to meter the silicone oil or other suitable release agent material to a desired thickness onto a metering roll. In the fusing of monochrome (i.e. black on a conventional imaging substrate) the uniformity of the oil layer on the metering roll is not so critical compared to that required for color toner images, particularly, those associated with transparency substrate materials used for optically projecting the color images.
Following is a discussion of prior art, incorporated herein by reference, which may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 4,214,549 granted to Rabin Moser on Jul. 29, 1980 discloses a RAM system comprising a donor roll comprising an outer layer fabricated from a heat insulative and deformable material, for example, silicone rubber which transfers functional release material from a metering roll a heated fuser roll. A metering blade is supported in contact with the metering roll for metering the release material onto the metering roll to a specified amount per copy. This type of RAM system dispenses a fixed amount of release agent material to the fuser roll member.
U. S. Pat. No. 5,504,566 granted to Chow et al on Apr. 2, 1996 discloses an apparatus for fusing toner images to a substrate. A Release Agent Management (RAM) system for applying silicone oil to a metering roll utilizes a pair of metering blades to improve oil uniformity on the metering roll. Thus, streaks or localized areas of excess silicone oil as the result of blade defects and/or dirt accumulation associated with a first blade, are metered or smoothed to a more uniform thickness by the second blade. To this end, the first metering blade serves to meter silicone oil to a first predetermined thickness while the second blade serves to meter oil streaks to a second predetermined thickness which is greater than the first predetermined thickness.
U. S. Pat. No. 5,212,527 granted to Fromm et al on May 18 discloses a release agent management (RAM) system including a metering roll supported for contact with release agent material contained in a sump. A donor roll is provided for applying oil deposited thereon by the metering roll. A metering blade structure for metering silicone oil onto the metering roll has two modes of operation. In one mode, a wiping action of a metering blade meters a relatively large quantity of silicone oil to the roll surface for accommodating the fusing of color toner images. In another mode of operation, a doctoring action is effected for metering a relatively small amount of silicone oil to the roll surface for accommodating the fusing of black toner images.
U.S. Pat. No. 5,625,859 granted to Rabin Moser on Apr. 29, 1997 discloses a method and apparatus for preventing oil streaks on color transparencies. To this end release agent material in the form of silicone oil is applied to a heated fuser roll using the metering roll of a two-roll RAM system. The silicone oil applied to the fuser roll is then metered to a uniform thickness with a metering blade contacting the surface of the heated fuser roll. The blade is adapted to be engaged with the fuser roll only during the fusing of process color images on transparency material in order to minimize wear of the blade and/or fuser roll surface and to minimize contamination of the blade due to unnecessary contact.
A release agent management system is disclosed in Xerox disclosure Journal, Vol. 3, Number 6, November/December 1978. As disclosed therein, the RAM system comprises a metering roll to which silicone oil is applied or metered using a pair of blades. The metering roll is disposed such that it can be rotated through silicone oil contained in a sump. A first metering blade is supported for contact with the roll in a position below a second metering blade. The first metering blade is mounted slightly above the fluid level of the silicone oil contained in the sump. By tandem mounting the two blades less frequent maintenance is required because there is double the area for toner or dirt accumulation. By such orientation of these blades, the device is less dependent upon a tall curtain of oil, thus allowing a minimum static height which minimizes potential sloshing problems when the machine containing the device is moved about. The blade serves to pre-meter a fixed amount of oil which can subsequently be precision metered to the roll by the second blade. Thus, a first thickness of oil is metered to a lesser thickness by the second blade.
U.S. patent application Ser. No. 08/936216 filed on Sep. 26, 1997 in the name of Condello et al relates to a Release Agent Metering (RAM) system including a metering roll and a pair of metering blades. is positioned in contact with a metering roll at a location intermediate, a nip formed through pressure contact of the metering roll with a donor roll, and a supply of release agent material such that as the metering roll is rotated in the imaging process direction release agent material is metered onto the metering roll and contaminants are prevented from getting deposited on the fuser roll. A second metering blade contacts the metering roll at a location that is intermediate the aforementioned nip and the supply of release agent such that when the metering roll is rotated in the direction opposite to the process direction excess release agent material and/or contaminants are prevented from being deposited on the fuser roll.